linux-kernel - [PATCH] tools lib traceevent: Mask higher bits of str addresses for 32-bit traces

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Date:	Thu, 17 Sep 2015 12:14:36 +0100
From:	Kapileshwar Singh <kapileshwar.singh@....com>
To:	linux-kernel@...r.kernel.org
Cc:	Kapileshwar Singh <kapileshwar.singh@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Javi Merino <javi.merino@....com>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>
Subject: [PATCH] tools lib traceevent: Mask higher bits of str addresses for 32-bit traces

When a trace recorded on a 32-bit device is processed with a 64-bit
binary, the higher 32-bits of the address need to be masked.

The lack of this results in the output of the 64-bit pointer
value to the trace as the 32-bit address lookup fails in find_printk.

Before:
burn-1778  [003]   548.600305: bputs:   0xc0046db2s: 2cec5c058d98c

After:
burn-1778  [003]   548.600305: bputs:	0xc0046db2s: RT throttling activated

The problem occurs in PRINT_FEILD when the field is recognized as a pointer
to a string (of the type const char *)

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Javi Merino <javi.merino@....com>
Cc: David Ahern <dsahern@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Reported-by: Juri-Lelli <juri.lelli@....com>
Signed-off-by: Kapileshwar Singh <kapileshwar.singh@....com>
---
 tools/lib/traceevent/event-parse.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index 4d885934b919..39163ea4a048 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -3829,6 +3829,17 @@ static void print_str_arg(struct trace_seq *s, void *data, int size,
 		if (!(field->flags & FIELD_IS_ARRAY) &&
 		    field->size == pevent->long_size) {
 			addr = *(unsigned long *)(data + field->offset);
+
+			/* In case the long_size is 4. The higher 32bits
+			 * need to be masked for a successful lookup in
+			 * in the printk table. As the pointers are 32-bit
+			 * long. This could happen if a trace recorded on
+			 * 32-bit platform is processed using a 64-bit
+			 * binary
+			 */
+			if (pevent->long_size == 4)
+				addr = addr & 0xffffffff;
+
 			/* Check if it matches a print format */
 			printk = find_printk(pevent, addr);
 			if (printk)
-- 
1.9.1

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